Aqueous dispersions containing cyclopolymer dispersants

ABSTRACT

PCT No. PCT/US94/08645 Sec. 371 Date Jan. 25, 1996 Sec. 102(e) Date Jan. 25, 1996 PCT Filed Jul. 29, 1994 PCT Pub. No. WO95/04109 PCT Pub. Date Feb. 9, 1995Aqueous dispersions which are particularly well suited for use as aqueous jet ink compositions having an aqueous carrier medium which comprises water or a mixture of water and at least one organic solvent, a particulate solid, preferably a pigment, and a cyclopolymer dispersant.

FIELD OF THE INVENTION

This invention relates to aqueous dispersions having excellentstability. In a preferred embodiment, this invention relates to aqueouspigmented inks for ink jet printers wherein the pigment dispersant is acyclopolymer.

BACKGROUND OF THE INVENTION

Water-based pigment dispersions are well known in the art, and have beenused commercially for applying films, such as paints, to varioussubstrates. The pigment dispersion is generally stabilized by either anon-ionic or ionic technique. When using the non-ionic technique, thepigment particles are stabilized by a polymer that has a water-soluble,hydrophilic section that extends into the water and provides entropic orsteric stabilization. Representative polymers useful for this purposeinclude polyvinyl alcohol, cellulosics, ethylene oxide modified phenols,and ethylene oxide/propylene oxide polymers. While the non-ionictechnique is not sensitive to pH changes or ionic contamination, it hasa major disadvantage for many applications in that the final product iswater sensitive. Thus, if used in ink applications or the like, thepigment will tend to smear upon exposure to moisture.

In the ionic technique, the pigment particles are stabilized by apolymer of an ion containing monomer, such as neutralized acrylic,maleic, or vinyl sulfonic acid. The polymer provides stabilizationthrough a charged double layer mechanism whereby ionic repulsion hindersthe particles from flocculation. Since the neutralizing component tendsto evaporate after application, the polymer then has reduced watersolubility and the final product is not water sensitive.

Ideally, a polymer dispersant that provides both steric and chargeddouble layer stabilization forces would make a much more robust pigmentdispersion. Polymer dispersants having both random and block structureshave been disclosed for this purpose. For example, U.S. Pat. No.4,597,794 to Canon proposes an aqueous ink dispersion for ink jetprinters in which a pigment is dispersed by a polymer having ionichydrophilic segments and aromatic hydrophobic segments that adhere tothe pigment surface. U.S. Pat. No. 5,085,698 to Ma et al. discloses theuse of AB or BAB structured block polymers as pigment dispersants. Whilethe random polymer dispersants can be prepared readily by conventionalpolymerization techniques, the structured block polymer dispersantsgenerally offer improved dispersion stability. However, the structuredblock polymers usually require a more elaborate synthesis plan, moredemanding reaction conditions, and high raw materials purity, as in thecase of anionic polymerization and group transfer polymerization. A moreconvenient polymerization process, whereby desired structure may readilybe built into the polymer, is desired for more advanced high qualitydispersion applications such as ink jet printers.

Ink jet printing is a non-impact printing process wherein a digitalsignal produces ink droplets on media substrates, such as paper ortransparency films. In thermal ink jet printing, resistive heating isused to vaporize the ink, which is expelled through an orifice in theink jet printhead toward the substrate. This process is known as firing,in which water is vaporized by the heat, causing a very rapid anddrastic local compositional change and temperature rise. This occursrepeatedly at high frequency during the life of the printhead. Further,in the orifice areas, the ink composition can drastically change fromwater-rich to solvent-rich due to evaporation of water. This tends tocause the pigment particles to flocculate around the orifice in theprinthead, eventually leading to plugging of the orifice. Particleflocculation thus will cause misdirection of the ink drop, or preventthe drop to eject at all in extreme cases.

In conventional coating applications, many additives of organic natureare used to impart the desired physical properties for the final use.Examples include polymer binders, thickeners, thixotropic agents,coating aids, etc. During the drying process, these components areconcentrated. The pigment dispersion needs to accommodate such changesin order to maintain the uniformity and color quality for the finalcoatings.

Accordingly, the need exists for dispersants which can be prepared by aconvenient and inexpensive polymerization process, and will provideimproved dispersion stability for improved quality for applications suchas thermal ink jet printers.

SUMMARY OF THE INVENTION

The invention provides a dispersion having excellent stability, thedispersion containing an aqueous carrier medium, a particulate solid,and a cyclopolymer dispersant consisting essentially of at least onecyclopolymer having the formula: ##STR1## with the proviso that either(i) R₁ and R₂ are hydrophobic groups, and X and Y are hydrophilicgroups, or (ii) R₁ and R₂ are hydrophilic groups, and X and Y arehydrophobic groups. The dispersions have broad compatibility with watermiscible organic cosolvents, aqueous additives such as thickeners, latexemulsions, and the like. In a preferred embodiment, the particulatesolid is a pigment and the resulting dispersion is employed as an inkparticularly adapted for use in a thermal ink jet printer.

DETAILED DESCRIPTION OF THE INVENTION

The dispersions of this invention have excellent stability, and areparticularly suited for use as aqueous ink jet ink compositions for inkjet printers in general, and thermal ink jet printers in particular. Theinks may be adapted to the requirements of a particular ink jet printerto provide a balance of light stability, smear resistance, viscosity,surface tension, optical density, and crust resistance.

Aqueous Carrier Medium

The aqueous carrier medium is water or a mixture of water and at leastone water soluble and/or water-dispersable organic component. Deionizedwater is commonly used. The organic component may be an organic solvent,polymeric binder, thickener, thixotropic agent, coating aid or othercomponent conventionally used to adapt the dispersion to its intendedapplication.

For ink jet inks, the aqueous carrier medium is typically a mixture ofwater and at least one water-soluble organic solvent. Representativeexamples of water-soluble organic solvents are disclosed in U.S. Pat.No. 5,085,698. Selection of a suitable mixture of water and watersoluble organic solvent depends upon requirements of the specificapplication, such as desired surface tension and viscosity, the selectedpigment, drying time of the pigmented coating or ink jet ink, and thetype of media substrate onto which the coating or ink will be printed. Amixture of diethylene glycol and deionized water is preferred as theaqueous carrier medium for ink jet inks, with the composition typicallycontaining between 30% and 95% (preferably 60% to 95%) water by weight,based on the total weight of the aqueous carrier medium.

Particulate Solids

The particulate solid may be a pigment, colloidal silver halide,metallic flake, a herbicide, an insecticide, or biomaterial such as adrug, or other solid depending upon the particular application of thedispersion. For example, if the intended use is in an ink or a paint,the particulate solid is a pigment or a mixture of two or more pigments.The term "pigment" as used herein means a colorant that is insoluble inthe aqueous carrier medium.

Most particulate solids have functional groups on their surface, whichare capable of "binding" with "binding sites" on the hydrophobic side ofthe selected cyclopolymer as discussed hereinafter. For example, carbonblack particles typically have chemisorbed oxygen complexes on theirsurfaces, which are primarily acidic in nature; namely, the surface willhave carboxylic, quinonic, lactonic, or phenolic groups to varyingdegrees that depend on manufacturing conditions. These acidic groups onthe pigment surface provide binding sites for dispersants with basicfunctions, such as amine groups. With other pigments having acidicsurfaces or basic surfaces, which are equally useful in this invention,either the pigment itself contains functional groups or the pigmentsurfaces have been modified by compounds containing functional groupssuch as sulfonic, phosphoric, and carboxylic acid groups or amine typeof basic groups. Furthermore, almost all of the organic color pigmentsand many of the surface treatment compounds have aromatic features intheir structures, providing sites for additional aromatic interactionswith the dispersant. Examples of pigments which may be used to form thecomposition include azo, anthraquinone, thioindigo, oxazine,quinacridone, lakes and toners of acidic dye stuffs or basic dye stuffs,copper phthalocyanine and its derivatives, and various mixtures andmodifications thereof.

The particle size and density of the particulate solid, and viscosity ofthe aqueous carrier medium, will have an influence on the dispersionstability. Brownian motion of minute particles will help prevent theparticles from flocculation and settling. While the selected particlesize thus will vary with the selected cyclopolymer dispersant, particledensity, and other requirements of the specific application, particlesas large as 30 microns may be selected for some applications.

For ink jet ink applications, the pigment particles need to besufficiently small to permit free flow of the ink through the ink jetprinting device, especially at the ejecting nozzles that typically havea diameter ranging from 10 to 50 microns. In addition, it is alsodesirable to use small particles for maximum color strength and gloss.The range of useful particle size is typically 0.005 to 15 microns,preferably 0.005 to 1 micron.

Also in the case of pigments, the selected pigment may be used in dry orwet form. For example, pigments are usually manufactured in aqueousmedia and the resulting pigment is obtained as water wet presscake. Inpresscake form, the pigment is not aggregated to the extent that it isin dry form. Thus, pigments in water wet presscake form do not requireas much deaggregation in the process of preparing the inks from drypigments. Representative useful commercial dry and presscake pigmentsare disclosed in the aforementioned U.S. Pat. No. 5,085,698.

Fine particles of metal or metal oxides (such as copper, iron, steel,aluminum, silica, alumina, titania, and the like) also may be used topractice the invention and may find applications in the preparation ofmagnetic ink jet inks and other coating applications for the electronicindustries. Disperse dyes, which are aqueous carrier medium insolublecolorants, may be dispersed using the cyclopolymer dispersants of theinvention.

Cyclopolymer Dispersant

The cyclopolymer dispersant has a hydrophilic section containing groupssoluble in the aqueous carrier medium, and a hydrophobic section thatbinds with the selected particulate solid. These two sections aresituated on the opposite sides of the polymer backbone as depicted inthe following formula: ##STR2## wherein (i) R₁ and R₂ are hydrophobicgroups, and X and Y are hydrophilic groups, or (ii) R₁ and R₂ arehydrophilic groups, and X and Y are hydrophobic groups. The degree ofpolymerization (n) is such that the weight average molecular weight ofthe polymer is in the range of 1,000 to 50,000, and preferably less than20,000. For ink jet ink applications, the weight average molecularweight typically is less than 10,000.

As stated above, R₁ and R₂ may be hydrophobic or hydrophilic, dependingon the particular substituent that is selected. In general, R₁ and R₂are independently selected from the group consisting of COOR, CN,C(O)NHR₄ and C(O)NR₅ R₆ wherein R, R₄, R₅, and R₆ are independentlyselected from the group consisting of alkyl, substituted alkyl, aryl, orsubstituted aryl groups having 1 to 18 carbon atoms when the sidecontaining R₁ and R₂ is used as the hydrophobic pigment binding side; orR₁ and R₂ may be independently selected from the group consisting ofCOOH, COOR₇, C(O)NHR₈, and C(O)NR₉ R₁₀ wherein R₇, R₈, R₉ and R₁₀ areindependently selected from the group consisting of alkyl, aryl,aralkyl, or alkylaryl group containing 1 to 30 carbon atoms andsufficient hydrophilic groups (e.g., hydroxy or ether groups) to renderthe side containing R₁ and R₂ as a whole hydrophilic, or preferablywater soluble, when it is used as the hydrophilic side. A useful exampleof the hydrophilic groups for R₇ through R₁₀ includes (CH₂ CH₂ O)_(m) Hwherein m=1 to 15.

As stated above, X and Y are selected such that they are hydrophilicwhen R₁ and R₂ are hydrophobic, or hydrophobic when R₁ and R₂ arehydrophilic.

In general, when X and Y are hydrophobic they are independently selectedfrom the group consisting of COOR, CN, R₃ CO, C(O)NHR₄, and C(O)NR₅ R₆wherein R, R₄, R₅, and R₆ are defined as above and R₃ is an alkyl groupcontaining 1 to 6 carbon atoms when the side containing X and Y is usedas the hydrophobic pigment binding side. Or, when X and Y arehydrophilic they are independently selected from the group consisting ofCOOH, PO₃ H, SO₃ H, COOR₇, C(O)NHR₈, C(O)NR₉ R₁₀, and R₁₁ CO wherein R₇,R₈, R₉, R₁₀ and R₁₁ are independently selected from the group consistingof alkyl, aryl, aralkyl or alkylaryl group containing 1 to 30 carbonatoms and sufficient hydrophilic groups (e.g., hydroxy or ether groups)to render the side containing X and Y as a whole hydrophilic orpreferably water soluble when it is used as the hydrophilic side. Auseful example of the hydrophilic groups for R₇ through R₁₁ includes(CH₂ CH₂ O)_(m) H wherein m=1 to 15.

X and Y, together with the carbon atom to which they are attached, mayform a carbocyclic or heterocyclic ring system. Suitable ring systemsinclude a dimedone ring or 1,3-dioxan-4,6-dione ring, a barbituric acidring, a 3-alkyl-isoxazol-5(4H)-ring or a 3-aryl-isoxazol-5(4H)-one ring.Substituents on the ring may be hydrophilic or hydrophobic in nature, asdiscussed above.

The term "substituted" alkyl or aryl as used herein means an alkyl oraryl group that contains one or more substituents that do not interferewith the polymerization process. Such substitutents may include alkyl,hydroxy, amino, ester, acid, acyloxy, amide, nitrile, halogen,haloalkyl, alkoxy, epoxide, nitro, thioether, sulfonyl ester,sulfonamide, silyloxy, alkylsilyl.

To solubilize the hydrophilic side into the aqueous carrier medium, itmay be necessary to make salts of the acid groups contained in thisside. Salts of the acid groups are prepared by neutralizing withneutralizing agents. For example, the neutralizing agent may be anorganic base such as amines; alkanol amines; pyridine; ammoniumhydroxide or tetraalkyl ammonium hydroxide; an alkali metal hydroxidesuch as potassium, sodium or lithium hydroxide; carbonates, suchpotassium carbonate; and bicarbonates, such as potassium bicarbonate.

As mentioned above, the hydrophobic side of the cyclopolymer has"binding sites" that bind with the particulate solid. By "binding" it ismeant that physical attraction is achieved between the particulate solidand cyclopolymer dispersant, generally without permanent chemicalbonding. A first way that this binding may occur is through hydrophobicinteractions wherein the cyclopolymer has substituents that are the sameas those contained in or on the surface of the particulate solid.Pigment particles, for example, may be pretreated with substances whichrender the surface hydrophobic. The hydrophobic side of the cyclopolymercan bind to such surface through hydrophobic interactions.

A second way in which a cyclopolymer can bind to a solid particulate isthrough aromatic interactions. If the particulate solid containsaromatic or aromatic-like groups, or if its surface has been pretreatedwith an aromatic substance, then the aromatic groups in the hydrophobicside can further improve the binding force to the solid particulate.

A third way in which a cyclopolymer can bind to a particulate solid isthrough ionic bonds. For example, a solid particulate containingsulfonic acid groups can bind strongly to a cyclopolymer in whichhydrophobic pigment binding side of the polymer contains amine groups.Similarly, a pigment containing quaternary ammonium groups can bind to acyclopolymer through acid groups.

Covalent bonding provides a fourth, and especially strong, mode ofbinding a cyclopolymer dispersant to a particulate solid. For example, aparticulate solid with carboxylic groups will react with a polymer whichcontains epoxy groups to form ester linkages. Thus, a cyclopolymertailored to contain glycidyl methacrylate groups in the hydrophobic sidewill form permanent chemical links to a carboxylic acid-containingparticulate solid.

The cyclopolymers can be easily prepared by techniques familiar to thoseskilled in the art, for example free radical polymerization. Themolecular weight readily may be controlled by techniques well known inthe art, such as the use of chain transfer agents, choice ofpolymerization solvent and temperature, amount of polymerizationinitiator, etc. They are prepared from 4,4-disubstituted 1,6-dienes ofthe following formula: ##STR3## wherein R₁, R₂, X, and Y are defined asthose corresponding groups in the polymers structure above. Thesedisubstituted dienes may be synthesized by reacting a compound X-CH₂ -Ywith two or more molar equivalents of a compound H₂ C═C(R₁)CH₂ A in thepresence of an organic or inorganic base, wherein A is a substituentthat is removed during the reaction, such as a halide group. In thiscase, the diene contains two identical R groups (i.e., R₁ and R₂ are thesame). Alternatively, compound X-CH₂ -Y may be reacted with one molarequivalent of the compound H₂ C═C(R₁)CH₂ A, followed by reaction withone molar equivalent of the compound H₂ C═C(R₂)CH₂ A, in the presence ofan organic or inorganic base, to form a diene having different R groups.

The 4,4-disubstituted 1,6-diene monomers may be copolymerized with aminor amount of other types of monomers to modify the physicalproperties such as glass transition temperature (Tg) or thehydrophobicity/hydrophilicity balance for optimal dispersing propertiesof the polymer. Either hydrophobic or hydrophilic monomers may be used.Useful monomers may include for example acrylates, methacrylates,vinylaromatics, and acrylamides. Examples of such monomers are acrylicacid, methacrylic acid, methyl acrylate, ethyl acrylate, n-butylacrylate, t-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate,ethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate,2-ethylhexyl methacrylate, cyclohexyl methacrylate, phenyl acrylate,benzyl acrylate, phenyl methacrylate, benzyl methacrylate, 2-phenylethylmethacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,hydroxypropyl acrylate, styrene, δ-methylstyrene, vinylpyridine,N-vinylpyrrolidone, vinyl carbazole, vinyldene halide, andacrylonitrile.

Additives

Depending on the requirements for the intended application, varioustypes of additives can be used to modify the properties of these solidparticulate dispersions. Examples include organic cosolvents, coalescingagents, polymeric binders including the water soluble polymers and thewater dispersable latex emulsions, thickeners, thixotropic agents,surfactants, coating aids, biocides, sequestering agents, etc.

When used in ink jet ink applications, the aqueous dispersions maycontain anionic, cationic, nonionic, or amphoteric surfactants in theamount of 0.01-5% and preferably 0.2-2%, based on the total weight ofthe ink. Biocides such as Dowicides® (Dow Chemical, Midland, Mich.),Nuosept® (Huls America, Inc., Piscataway, N.J.), Omidines® (Olin Corp.,Cheshire, Conn.), Nopcocides® (Henkel Corp., Ambler, Pa), Troysans®(Troy Chemical Corp., Newark, N.J.), and sodium benzoate; sequesteringagents such as EDTA; and other known additives, such as humectants,viscosity modifiers and other polymers may also be added to improvevarious properties of the ink compositions.

The dispersion of aqueous carrier medium, particulate solid, andcyclopolymer dispersant is prepared using conventional technique(s)known in the art. For example, a pigment dispersion may be prepared bypremixing the selected pigment(s) and the polymer in water. Thedispersion step may be accomplished in a horizontal mini mill, a ballmill, an attritor, or by passing the mixture through a plurality ofnozzles within a liquid jet interaction chamber at a liquid pressure ofat least 1000 psi to produce a uniform dispersion of the pigmentparticles in the aqueous carrier medium. It is generally desirable tomake the pigmented ink jet ink in concentrated form, which issubsequently diluted with a suitable liquid to the appropriateconcentration for use in the ink jet printing system. By dilution, theink is adjusted to the desired viscosity, color, hue, saturationdensity, and print area coverage for the particular application.

The preferred formulation in an ink jet ink composition is:

(a) aqueous carrier medium present in the amount of approximately 70% to96%, preferably approximately 80% to 96, based on total weight of theink when an organic pigment is selected; and approximately 25% to 96%,preferably approximately 70% to 96% when an inorganic pigment isselected;

(b) pigments present in the amount of up to approximately 30% pigment byweight for organic pigments, but generally in the range of approximately0.1 to 15%, and preferably approximately 0.1 to 8%, by weight of thetotal ink composition. With inorganic pigments (which have higherspecific gravities), higher concentrations are employed, and they may beas high as 75% in some cases;

(c) cyclopolymer present in the amount of approximately 0.1 to 30% byweight of the total ink composition, preferably in the range ofapproximately 0.1 to 8% by weight of the total ink composition.

Many ink performance features such as the drop velocity, separationlength of the droplets, drop size, and stream stability are greatlyaffected by the surface tension and the viscosity of the ink. Pigmentedink jet inks suitable for use with ink jet printing systems should havea surface tension in the range of about 20 dyne/cm to about 70 dyne/cmand, more preferably, in the range of 30 dyne/cm to about 70 dyne/cm at20° C. Acceptable viscosities are no greater than 20 cP, and preferablyin the range of about 1.0 cP to about 10 cP at 20° C.

Industrial Applicability

The dispersions of this invention may be designed to provide excellentstability for organic and inorganic solids in aqueous media or mixedaqueous-organic media. The dispersions are particularly useful forcoating applications such as paints and color films for imagingapplications. They are also very useful for various types of inks.

EXAMPLES

This invention will now be further illustrated, but not limited, by thefollowing examples.

Procedure 1

2,6-dibenzyloxycarbonyl-4,4-di-(t-butoxycarbonyl)1,6-heptadiene monomerwas prepared using the following procedure:

To a cooled suspension of sodium hydride (5.12 g, 0.17 mol. dispersionin oil about 80% grade) in acetonitrile (300 mL), was added di-t-butylmalonate (14.78 g, 0.0684 mol). The resulting mixture was stirred at 4°C. for 15 minutes before a solution of benzyl 2-(bromomethyl)propenoate(34.9 g, 0. 137 mol) in acetonitrile (100 mL) was added. Benzyl2-(bromomethyl)propenoate was obtained from the bromination reaction ofthe Bayliss-Hillman reaction product which was prepared with benzylacrylate and paraformaldehyde in the presence of DABCO (1,4-diazabicyclo[2.2.2]octane). (¹ H-NMR (CDCl₃) δ (ppm): 4.20 (s, 2H); 5.25 (s, 2H);6.00 (s, 1H); 6.40 (s, 1H); and 7.40 (br. s, 5H)). The reaction mixturewas then stirred at room temperature for 2 hours. Saturated sodiumchloride solution (200 mL) was added and the mixture was extracted threetimes with diethyl ether (600 mL in total). The combined organic phasewas washed with water, then brine. After drying over anydrous sodiumsulfate, filtration and evaporation to dryness, it was chromatographedin a silica gel column (Merck 60, 70-230 mesh; 10% diethyl ether inpetroleum spirit as eluent) to give the title compound (16.9 g, 44%yield) as a viscous colorless liquid. ¹ H-NMR (CDCl₃) δ (ppm): 1.45 (s,18H); 2.98 (s, 4H); 5.15 (s, 4) 5.75 (s, 2H); 6.30 (s, 2H); and 7.35(br. s, 10H).

Procedure 2

A cyclopolymer was prepared from2,6-dibenzyloxycarbonyl-4,4-di-(t-butoxycarbonyl)-1,6-heptadiene monomerusing the following procedure. The resulting polymer has hydrophilicgroups (carboxylic acid) and hydrophobic aromatic groups (benzyl ester)on the opposite sides of the cyclohexane polymer backbone. It wasprepared by free radical cyclopolymerization of the monomer, followed byhydrolysis reaction to convert the t-butoxycarbonyl groups to thecarboxylic acid groups.

The monomer,2,6-dibenzyloxycarbonyl-4,4-di(t-butoxycarbonyl)-1,6-heptadiene (15.4 g,27.2 mol), and initiator α, α'-azobisisobutyronitrile (AIBN) (223 mg,1.36 mol, 5% molar) were dissolved in o-xylene (270 mL). The mixture wasdegassed three times under vacuum (0.005-0.001 mm Hg) in a Young vessel.It was heated at 60° C. for 20 hours, followed by additional 2 hours at90° C. After cooling, the polymer was precipitated with methanol andfiltered to give 10.4 g (67% isolated yield) of a white powder. GPC(polystyrene as the standard): Mn=6064; Mw=12773; Mw/Mn=2.10.

The cyclopolymer (10.0 g) was then mixed with formic acid (70 mL) indichloromethane (140 mL). The solution was refluxed for 18 hours. Aftercooling, the hydrolyzed product (7.82 g, 98% isolated yield) wasisolated. ¹ H-NMR (Acetone-d6) showed complete loss of t-butyl group.

The cyclopolymer (7.22 g) was dissolved with potassium hydroxide (3.08g, 46.6% solution) in deionized water (69.2 g) to give a clear 9.0%neutralized cyclopolymer solution.

Procedure 3

A pigment dispersion was prepared using a cyclopolymer prepared inProcedure 2 as follows:

    ______________________________________                                                              Amount                                                  Ingredient            (parts by weight)                                       ______________________________________                                        FW18, Carbon black pigment                                                                          16                                                      (Degussa Corp. Allendale, NJ 07041)                                           Neutralized cyclopolymer solution,                                                                  79.5                                                    (9% solution)                                                                 Deionized water       63.8                                                    Total                 159.3                                                   ______________________________________                                    

The above mentioned components were premixed in a plastic beaker bymechanical stirring until no lumps or dry clumps were visible. Themixture was dispersed in a microfluidizer (Microfluidics Corp., Watham,Mass.) by passing it through the interaction chamber 5 times under aliquid pressure of about 7,000 psi. The resulting pigment dispersion had10% pigment concentration with an average particle size of 120 nm asdetermined by Brookhaven BI-90 particle sizer. The dispersion wasfiltered through a 1 micron high efficiency filter bag (3M FiltrationProducts, St. Paul, Minn. 55144-1000). The final pH was 10.8.

Ink Test

The pigment dispersion concentrate (10%) from Procedure 3 was letdownwith a vehicle solution to give the following composition.

    ______________________________________                                                               Amount                                                 Ingredient             (parts by weight)                                      ______________________________________                                        Carbon Black, FW18, (Degussa                                                                         4.0                                                    Corp., Allendale, NJ)                                                         Cyclopolymer from Procedure 2                                                                        1.8                                                    2-Pyrrolidone (Aldrich Chemical                                                                      3.0                                                    Co., Milwaukee, WI)                                                           N-Methylpyrrolidone (Aldrich                                                                         2.0                                                    Chemical Co., Milwaukee, WI)                                                  Liponic EG-1 (Lipo Chemicals, Inc.,                                                                  3.0                                                    Patterson, NJ)                                                                Zonyl FSA (DuPont Co., Wilmington,                                                                   0.05                                                   DE)                                                                           Deionized water        82.2                                                   ______________________________________                                    

The ink was filled into a thermal ink jet pen and printed with a HewlettPackard DeskJet ink jet printer (Hewlett Packard Co., Palo Alto, Calif.)on Gilbert bond paper (25% cotton, Mead Co., Dayton, Ohio). It printedsmoothly and the print had an extremely high optical density of 1.58 andsharp edges. The print was waterfast immediately after drying.

The ink stability was determined by measuring the particle size changeby Brookhaven BI-90 particle sizer (Brookhaven Instrument Corp.,Holtsville, N.Y. 11742) after the ink sample had been subjected to 4temperature cycles, each consisting of 4 hours at -20° C. and 4 hours at70° C. The above ink showed no significant change.

What is claimed is:
 1. A dispersion comprising an aqueous carriermedium, a particulate solid, and a cyclopolymer dispersant consistingessentially of at least one cyclopolymer having the formula: ##STR4##with the proviso that either (i) R₁ and R₂ are hydrophobic groups, and Xand Y are hydrophilic groups, or (ii) R₁ and R₂ are hydrophilic groups,and X and Y are hydrophobic groups; and n is selected such that theweight average molecular weight of the cyclopolymer is in the range of1,000 to 50,000.
 2. The dispersion of claim 1 wherein R₁ and R₂ arehydrophobic groups independently selected from the groups consisting ofCOOR, CN, C(O)NHR₄ and C(O)NR₅ R₆ wherein R, R₄, R₅, and R₆ areindependently selected from the group consisting of alkyl, substitutedalkyl, aryl, or substituted aryl groups having 1 to 18 carbon atoms,wherein the substituted group is a substituent that does not interferewith the polymerization process.
 3. The dispersion of claim 2 wherein Xand Y are hydrophilic groups independently selected from the groupconsisting of COOH, PO₃ H, SO₃ H, COOR₇, C(O)NHR₈, C(O)NR₉ R₁₀, and R₁₁CO wherein R₇, R₈, R₉, R₁₀ and R₁₁ are independently selected from thegroup consisting of alkyl, aryl, aralkyl or alkylaryl group containing 1to 30 carbon atoms and sufficient hydrophilic groups to render X and Yas a whole hydrophilic.
 4. The dispersion of claim 1 wherein R₁ and R₂are hydrophilic groups independently selected from the group consistingof COOH, COOR₇, C(O)NHR₈, and C(O)NR₉ R₁₀ wherein R₇, R₈, R₉ and R10 areindependently selected from the group consisting of alkyl, aryl, aralkylor alkylaryl group containing 1 to 30 carbon atoms and sufficienthydrophilic groups to render the R₁ and R₂ as a whole hydrophilic. 5.The dispersion of claim 4 wherein X and Y are hydrophobic groupsindependently selected from the group consisting of COOR, CN, R₃ CO,C(O)NHR₄, and C(O)NR₅ R₆ wherein R, R₄, R₅, and R₆ are independentlyselected from the group consisting of alkyl, substituted alkyl, aryl, orsubstituted aryl groups having 1 to 18 carbon atoms and R₃ is an alkylgroup containing 1 to 6 carbon atoms, wherein the substituted group is asubstituent that does not interfere with the polymerization process. 6.The dispersion of claim 1 wherein said particulate solid is a pigment.7. The dispersion of claim 6 wherein said pigment has a particle size inthe range of 0,005 to 15 microns.
 8. The dispersion of claim 1 whereinsaid dispersion is an ink jet ink containing 70 to 96% aqueous carriermedium, up to 30% by weight of an organic pigment, up to 75% by weightof an inorganic pigment, and 0.1 to 30% by weight cyciopolymerdispersant.
 9. The dispersion of claim 1 containing at least oneadditive selected from the group consisting of organic solvents,polymeric binders, water-soluble polymers, water-dispersible latexemulsions, thickeners, coalescing agents, surfactants, biocides,sequestering agents, thixotropic agents and coating aids.